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Synthesis, crystal structure and crystal-chemistry of ferri-clinoholmquistite, Li2Mg2Fe3Si8O22(OH)2. (Articolo in rivista)
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- Synthesis, crystal structure and crystal-chemistry of ferri-clinoholmquistite, Li2Mg2Fe3Si8O22(OH)2. (Articolo in rivista) (literal)
- Anno
- 2004-01-01T00:00:00+01:00 (literal)
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Iezzi G.; Cámara F.; Della Ventura G.; Pedrazzi G.; Oberti R.; Robert J-L. (2004)
Synthesis, crystal structure and crystal-chemistry of ferri-clinoholmquistite, Li2Mg2Fe3Si8O22(OH)2.
in Physics and chemistry of minerals
(literal)
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- Iezzi G.; Cámara F.; Della Ventura G.; Pedrazzi G.; Oberti R.; Robert J-L. (literal)
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- ISI Web of Science (WOS) (literal)
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- G. Iezzi
Bayerisches GeoInstitut, University of Bayreuth, Germany
F. Ca´mara Æ R. Oberti
CNR-Istituto di Geoscienze e Georisorse, Sezione di Pavia,
via Ferrata 1, 27100 Pavia, Italy
G. Della Ventura (&)
Dipartimento di Scienze Geologiche, Universita` di Roma Tre,
Largo S. Leonardo Murialdo 1, 00146, Roma, Italy
e-mail: dellaven@uniroma3.it
Tel.: +39-06-54888020
Fax: +39-06-54888201
G. Pedrazzi
Dipartimento di Sanita` Pubblica, Sezione di Fisica,
INFM Universita` di Parma, Via Volturno, 39,
43100 Parma, Italy
J-L Robert
ISTO, UMR 6113, 1A, Rue de la Fe´ rollerie,
45071 Orle´ans Cedex 2, France (literal)
- Titolo
- Synthesis, crystal structure and crystal-chemistry of ferri-clinoholmquistite, Li2Mg2Fe3Si8O22(OH)2. (literal)
- Abstract
- This work reports the synthesis of ferri-clinoholmquistite,
nominally hLi2(Mg3Fe3+
2)Si8O22(OH)2, at
varying fO2 conditions. Amphibole compositions were
characterized by X-ray (powder and single-crystal)
diffraction, microchemical (EMPA) and spectroscopic
(FTIR, Mo¨ ssbauer and Raman) techniques. Under
reducing conditions (?NNO+1, whereNNO=Nickel-
Nickel oxide buffer), the amphibole yield is very high
(>90%), but its composition, and in particular the FeO/
Fe2O3 ratio, departs significantly from the nominal one.
Under oxidizing conditions (? NNO+1.5), the amphibole
yield is much lower (<60%, with Li-pyroxene
abundant), but its composition is close to the ideal stoichiometry.
The exchange vector of relevance for the
studied system is M2(Mg,Fe2+) M4(Mg,Fe2+) M2Fe3+
-1
M4Li)1, which is still rather unexplored in natural systems.
Amphibole crystals of suitable size for structure
refinement were obtained only at 800 ?C, 0.4 GPa and
NNO conditions (sample 152), and have C2/m symmetry.
The X-ray powder patterns for all other samples were
indexed in the same symmetry; the amphibole closest to
ideal composition has a = 9.428(1) A ? , b = 17.878(3) A ? ,
c = 5.282(1) A ? , b = 102.06(2)?, V = 870.8(3) A ? 3.
Mo¨ ssbauer spectra show that Fe3+ is strongly ordered at
M2 in all samples, whereas Fe2+ is disordered over the B
and C sites. FTIR analysis shows that the amount of
CFe2+ increases for increasingly reducing conditions.
FTIR data also provide strong evidence for slight but
significant amounts of Li at the A sites. (literal)
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